Switching circuit for magnetron beam switching tube



April 28, 1959 H. Moss 7 2,884,560

. SWITCHING CIRCUIT FOR MAGNETRON BEAM SWITCHING TUBE Filed April 1a, 1956 SWITCH 34 CLOSED AND SWITCHING STEPS START F/g.3

INVENTOR.

HILARY MOSS ATTORNEY United States Patent SWITCHING CIRCUIT FOR MAGNETRON BEAM SWITCHING TUBE Hilary Moss, Malveru, Pa., assignor to Burroughs Corporation, Detroit, Mich., a corporation of Michigan Application April 16, 1956, Serial No. 578,402

9 Claims. 01. 315-21 dt C' To increase this charging rate, current must be increased or the capacity to be charged must be reduced. However, the total time to charge to a given voltage can be further reduced by preliminary priming of a spade to a voltage nearer the desired value, before it must charge to final value. At the start of a beam switching step, the

switching grid adjacent to the stably held beam is driven in the negative voltage direction and causes the beam to fan out toward this grid and the adjacent spade. Beam current then strikes this spade, providing the above men tioned charging current and lowering the spades voltage. If this spade already has been primed to some voltage intermediate between its supply voltage and its beam hold voltage, this charging current can bring the spade on down to beam holding voltage in a much shorter time; thus cutting down the time required to switch the beam.

An object of this invention is to efiect the above de- 1 scribed improvement in a practical circuit for priming the spades as described.

Another object of this invention is to minimize the above limitations upon spade charging time of a magnetron beam switching tube by reducing the time required to charge a spade to a required voltage after a beam switching signal is received on a switching grid.

I In accordance with this invention there is provided a resistance member for each holding position of a magnetron beam switching tube, connected to the spade thereof at one end and to the target thereof at a first intermediate point, and connected through a conductive link from a second intermediate point thereon to the next spade in the direction of beam advancement, to conduct electrons to this next spade.

For a more detailed description of this invention, ref- States Patent No. 2,721,955 issued to Sin-pih Fan et al.,.

and entitled Multi-Position Beam Tube. By use of the crossed electric and magnetic fields of a magnetron type structure and of a number of electrodes in successive arrays around a cathode, this tube can provide a high-current electron beam to a plurality of output electrodes in rapid succession and with great reliability.

As shown in Fig. 1, a cylindrical magnet 21 encloses tube 20 and provides an axial magnetic field therethrough. Tube 20 contains a central axial cathode 22 surrounded by several concentric arrays of electrodes. On a circular locus nearest to the cathode are the beam forming and holding electrodes 23, called spade electrodes. Beyond the spade electrodes on another circular locus are the target electrodes 24, positioned peripherally on this circle so as to cover the inter-spade spaces and to collect beam current flowing into such spaces between spades. Intermediate between one edge of each spade and the near edge of each target proximate to that spade are the switching grid electrodes 25. These grids also are on a circular locus centered on the cathode 22.

With the cathode heated to electron emission temperature and a positive potential on the spade electrodes and target electrodes, the magnetic field from magnet 21 is above that value required for magnetron type cut-oil of current in the tube and no current will flow. However, if one of the spade electrodes is reduced in potential to about half its previous potential the voltage gradients within the tube are distorted and a beam will form. This electron beam grazes the low potential spade and strikes the adjacent target electrode. A small portion of the elec-' tron beam does flow to this spade. With a suitable series resistor interposed in the connection of each spade to its positive voltage supply, this small portion of the beam':

current produces an IR drop which enables the spade to hold the beam stably in place once it grazes that spade.-

Switching grid electrodes 25 upset this stablebeamholding condition when a suitable negative potential is applied to the grid which is in the same inter-spade space as is the beam. As this grid goes negatively from its positive bias, the beam fans out across the target elec-. trode and some of it strikes the next spade electrode. This fraction of beam current produces another IR voltage drop which lowers the potential of this next spade. With a sufficiently lowered potential on the next spade, the beam switches over to the next target. This switching action occurs at a very rapid rate, the time required to switch from one target to the next being in the order of one-tenth of a micro-second.

Fig. 2 shows tube 20 connected into circuitry embodying this invention. A voltage supply +E is connected to a common line 29, to which a plurality of resistance membets 3%) are connected. The other end of eachresistance member is connected to one of the spades 23 of tube 20.

At an intermediate point on each resistance member 30, a target 24 is connected. The target connected to a particular resistance member is the target adjacent to the spade which is also connected to the same resistance.

member and is on the side of this spade in the direction of electron beam advancement. point on each resistance member 30, and preferably adjustable in its point of contact, diodes 31 are'connected. The other end of each diode 31 is connected to the next spade, in the direction of beam advancement and in a polarity to conduct electrons from this other intermediate point to the spade. The resistance member is divided into portions 30a, 30b, and 30c as shown. 1

This field is several times the strength required for magnetron cut off in tube 20, so no electrons are reaching any of the outer electrodes.

In a typical embodiment, switching grids ZS are' connected into common sets of alternate grids, and a bail At another intermediate anced or push-pull switching circuit 32 is connected to these sets of alternate grids. Switching signal 33 is applied to the primary of transformer 32 and a balanced switching signal is produced on its secondary and applied to the switching grids 25. A bias voltage +V is applied through the center tap of this secondary winding.

With tube 20 cut ofi, nothing happens until starting switch 34 is momentarily closed, at time T as shown in Fig. 3. This lowers the voltage on the connected spade and a beam forms as shown in Fig. 2 and as described before. With beam current flowing through various portions of resistance member 30, the beam-receiving target is reduced in. voltage to voltage V shown in the graph of Fig. 3. Connecting diode 31 then becomes conductive and the portion of V;- which the variable contact 35 picks off, or K.V will appear as V on the next spade; thus lowering this next spade substantially from supply voltage +E.

The switching signal 33 applied to switching grids 25 then takes control and causes the beam to advance to the next clockwise position at time T as shown in Fig. 3. As the switching grid in the illustrated beam holding position starts the beam fanning out toward the next spade and this next spade begins to receive the beam current, the beam finds this spade already down to voltage K.V with a smaller voltage change to go. In a shorter time, charging current to this next spade has lowered it to beam holding voltage V, and the beam is held stably on the next target, lowering it to V' Again, the next diode 31 taps ofl? a portion of this voltage V' K.V and lowers the next spade by this voltage K.V When the next switching step occurs at time T the beam again finds a primed spade and quickly charges it to voltage V As the beam advances on around tube 20, each positions target and spade returns rapidly to supply voltage +E when the beam leaves them. Some of the voltage drop which a holding spade requires is generated by full beam current flowing through portions 30b and. 30c of resistance member 30, the remaining voltage drop still is generated by the holding spades share of beam current flowing through portion 30a, all portions of resistance member 30 can be of lower ohmic value. This results in smaller RC recovery time constants for these electrodes.

As a result, the charging current which returns these electrodes to voltage +E when the beam leaves can be larger and is able to charge the electrodes to +E. more quickly. This maintains the average voltage for all spades at a higher level than if this return to +E were slow, thereby maintaining total beam current at a higher level.

At each switching step initiated by switching signal 33, the beam finds the next spade toward which it is advancing already primed by a substantial voltage drop caused by beam current flowing through diode 31, so that the beam is required to charge that spade for only asmall voltage drop which can be done in less time. With less time required for each switching step, the switching frequency can be correspondingly increased. Additionally, the smaller ohmic value of spade resistors; which is allowed by the use of full beam current to produce some of the voltage drop for the holding spade lowers the time constants of the spade circuits and allows them to return to supply voltage -|-E faster than a series resistor of higher ohmic value would allow. Thus, switching frequency is not limited by the further problem of having the beam advance all the way around the tube and be at a given beam holding position again, before the spade for that position has returned to supply voltage +E. Such a situation would seriously lower the average spade voltage, thereby causing a lower total beam current, making the switching operation erratic and reducing the output.

As' shown in Fig. 4, cor l'ductivedevices other than ditype voltage drop. These resistors allow each spade to change voltage when this voltage drop occurs on the connected target. With this lowered voltage, the next spade is primed for the beam switching cycle, and beam current can very quickly bring that spade on down to beam holding voltage.

What is claimed is:

1. A switching circuit for a magnetron beam switching tube which tube has a plurality of beam holding positions and each position includes a spade electrode, a target electrode and a switching electrode; said circuit comprising a plurality of resistance members commonly connected at one end for connection to a voltage supply and each connected at the other end to one of said spade electrodes and connected at an intermediate point to the one of said target electrodes adjacent to the connected spade electrode on the side of the direction of beam advancement, a plurality of diodes each connected from a point in one resistance member between said intermediate point and the common connection to the spade connected I end of the next resistance member in the direction of beam advancement, and a push-pull source of alternating voltage connected to said switching grids in common sets of alternate grids.

2. In a device using a magnetron beam switching tube which includes a plurality of beam holding positions and connection to a power supply, each connected at the other end to one of said spades and connected at a first intermediate point to the target adjacent to the connected spade in the direction of beam advancement, a plurality of diodes each conneced from a second intermediate point on a resistance member to the space connected end of the next resistance member in the direction of beam advancement to conduct electrons to said next resistance member, and a balanced source of alternating voltage and positive bias connected to sets of alternate switching grids. v

3. In the connecting circuitry for a magnetron beam switching tube having pluralities of spades, targets and switching grids, a spade voltage priming circuit comprising a resistance member for each beam holding position of said tube, connected to the spade thereof at one end and to the target thereof at a first intermediate point, and a diode connected from a second intermediate point thereon to the next spade in the direction of beam advancement to conduct electrons to said next spade.

4. A switching circuit comprising a magnetron beam switching tube including a plurality of beam holding positions with each position having a spade, a target and a switching electrode, a plurality of resistance members connected one to each of said spade electrodes and connected at a fixed intermediate point to the target associated with said connected spade in a beam holding position, a voltage supply commonly connected to all resistance members, a plurality of diodes connected to a variable intermediate point on each resistance member and to the next resistance member in the direction of beam advancement, and a source of switching signals connected in a balanced manner to alternate sets of said switching grids and to a bias voltage of said voltage supply.

5. In the connecting circuitry for a magnetron beamswitching tube having pluralities of spades, targets and switching grids, aspade voltage controllingcircuit comprising a first'plurality of resistors connected. one to each i assggeeo target of said tube, current conductive means connected from an intermediate point on each of said resistors to an adjacent spade in the direction of beam advancement in said tube, and a second plurality'of resistors connected from each spade to the adjacent target in the direction of beam advancement in said tube.

6. In the connecting circuitry for a magnetron beam switching tube having pluralities of spades, targets and switching grids, a spade voltage controlling circuit comprising a first plurality of current conductive means connected one to each target of said tube, a second plurality of current conductive means connected from a point on each of said first current conductive means to an adjacent spade in the direction of beam advancement in said tube, and a third plurality of current conductive means connected from each spade to the adjacent target in the direction of beam advancement in said tube.

7. A switching circuit for a magnetron beam switching tube which tube has a plurality of beam holding positions and each position includes a spade electrode, a target electrode and a switching electrode, said circuit comprising a plurality of resistance members commonly connected at one end for connection to a voltage supply and each connected at the other end to one of said spade electrodes and connected at an intermediate point to the one of said target electrodes adjacent to the connected spade electrode on the side of the direction of beam ad vancement, a plurality of diodes each connected from a point in one resistance member between said intermediate point and the common connection to the spade connected end of the next resistance member in the direction of beam advancement.

8. In the connecting circuitry for a magnetron beam switching tube having pluralities of spades, targets and switching grids, a spade voltage controlling circuit comprising a first plurality of resistors connected one to each target of said tube, direct current conductive means connected from an intermediate point on each of said re sistors to an adjacent spade in the direction of beam advancement in said tube, and a second plurality of resistors connected from each spade to the adjacent target in the direction of beam advancement in said tube.

9. In the connecting circuitry for a magnetron beam switching tube having pluralities of spades, targets and switching grids, a spade voltage controlling circuit comprising a first plurality of current conductive means connected one to each target of said tube, a second plurality of direct current conductive means connected from a point on each of said first current conductive means to an adjacent spade in the direction of beam advancement in said tube, and a third plurality of current conductive means connected from each spade to the adjacent target in the direction of beam advancement in said tube.

References Cited in the file of this patent UNITED STATES PATENTS 2,638,541 Wallmark May 12, 1953 

